1.3.1—The effects of systematic errors (including zero errors) and random errors

A systematic error shifts readings in a consistent direction, while random error causes scatter between repeated readings. A zero error is a systematic offset from a faulty zero.

Repeat measurements and average to reduce random variation; calibration, zero checks or a changed method address systematic bias. Repeats cannot remove a constant offset.

A balance reading 0.20 g with an empty pan adds 0.20 g to every mass unless corrected.

A precise cluster can still be inaccurate if it is systematically shifted.